Mr. Leek et V. Summers, REDUCED FREQUENCY-SELECTIVITY AND THE PRESERVATION OF SPECTRAL CONTRAST IN NOISE, The Journal of the Acoustical Society of America, 100(3), 1996, pp. 1796-1806
Reduced frequency selectivity associated with sensorineural hearing lo
ss may pose particular problems for hearing-impaired listeners in nois
y environments. In these situations, broader-than-normal auditory filt
ers may affect the perception of speech by reducing the contrast betwe
en spectral peaks and valleys in at least two ways. First, the peaks a
nd valleys in the internal representation of the speech spectrum becom
e smeared, resulting in less precise frequency analysis. Second, there
may be a reduction in the signal-to-noise ratio (S/N) at the output o
f each auditory filter. In order to examine the relationship between f
requency selectivity and identification of speechlike stimuli in noise
, hearing-impaired and normal-hearing listeners were trained to assign
vowel labels to four harmonic complexes which differed in the frequen
cy locations of four elevated (''peak'') harmonics. Peak harmonics wer
e chosen to approximate first- and second-formant frequencies in four
English vowels. Listeners were then tested to determine the spectral c
ontrast necessary between peak and background components in order to m
aintain identification accuracy in the presence of various levels of b
roadband noise. Results indicated that for these stimuli, normal-heari
ng listeners required about 1 dB of additional spectral contrast for e
very doubling of the intensity of noise. The required increase in spec
tral contrast was generally greater for listeners with broader-than-no
rmal auditory filters at 2000 Hz. This finding suggests indirectly tha
t in the internal representations of speech sounds embedded in noise,
the signal-to-noise ratio for listeners with abnormal frequency select
ivity is poorer than for listeners with normal frequency selectivity.
A poorer-than-normal internal S/N may be one factor underlying the com
mon observation that noise often is more degrading to speech understan
ding by hearing-impaired listeners than by normal-hearing listeners.